In recent years a number of minimally invasive technologies have been developed to treat arterial diseases, such as atherosclerosis, which result in narrowing and stenosis of body lumens, such as the coronary arteries. Specifically, a large number of endoluminal prostheses, often referred to as "stents," have been developed to maintain the patency of a vessel, following, for example, an balloon dilatation procedure (e.g., angioplasty). These devices generally are inserted percutaneously and transluminally to the site of a constricted region in a contracted delivery state. After being positioned at a desired deployment site, the stents are then permitted to self-expand, or are balloon dilated to support the vessel or body lumen.
A drawback encountered with many previously known stents is the inability to precisely control the placement of the stent during deployment. For example, coiled sheet stents, such as described in U.S. Pat. No. 5,443,500 to Sigwart, are constrained in a contracted delivery state by a locking wire or exterior sheath, and deployed by removing the wire or retracting the sheath proximally. A disadvantage of these deployment mechanisms, however, is that the distal end of the stent expands while the proximal end is still constrained, and may result in cocking or longitudinal movement of the stent during deployment.
Similar types of stent motion may be encountered in deploying helical spring-type stents, such as described in U.S. Pat. No. 4,553,545 to Maass et al. It would therefore be desirable to provide a stent delivery system and methods that enable portions of a stent to be deployed in a predetermined sequence along the length of the stent, thereby minimizing the risk for cocking or displacement of the stent during deployment.
A further disadvantage of retractable-sheath delivery systems is that the exterior sheaths increase the overall diameter of the delivery system and reduce the ability of the delivery system to negotiate tortuous anatomy. It would therefore be desirable to provide a stent delivery system and methods that permit the thickness of an exterior sheath of the delivery system to be reduced or eliminated altogether.